Pressed on the preparations, Mr Hoban added that the Treasury was “contingency planning for a whole range of outcomes”.

Asked if the Coalition would rule out ever joining the euro, Mr Hoban replied: “I don’t think there is any intention for us to join the euro at a time when it is breaking up.”

Treasury officials insisted that he had been speaking conditionally and had not meant that the euro was fragmenting.

However, eurozone leaders publicly admitted that the exit of some euro members was now possible.

“We would like Greece to remain a member but we’re not saying Greece has to stay a member at all costs,” said Jean-Claude Juncker, prime minister of Luxembourg and chairman of the eurozone finance ministers.

Jean Leonetti, France’s minister for Europe, said that if Greece did not accept the terms of an EU bail-out, it would have to leave the single currency. “You can’t have the solidarity of 17 countries without the obligations, the budgetary discipline,” he said. If not “the country goes bankrupt, and has to leave the eurozone”.

European leaders have never previously discussed an exit, because the treaties that created the euro contain no provision for members to leave.

As the debt crisis has continued, the lack of clear exit rules has become a source of concern for investors.

Some economists warn that if a member like Greece was forced out in chaotic circumstances, the single currency itself could be threatened as there would be no widely-agreed rules on how to value assets and investments priced in euros.

The European Commission yesterday confirmed that because there are no clear euro exit rules, any member leaving the single currency would also have to leave the EU itself.